Flame retardant adhesive composition, and adhesive sheet, coverlay film and flexible copper-clad laminate using same

ABSTRACT

The present invention provides a halogen-free, flame retardant adhesive composition that exhibits excellent anti-migration properties, not only within single layer structures, but also within multilayer structures of much higher density. The flame retardant adhesive composition according to the present invention comprises: (A) a halogen-free epoxy resin, (B) a carboxyl group-containing acrylic resin and/or a carboxyl group-containing acrylonitrile-butadiene rubber, (C) a curing agent, (E) a specific polyphosphoric acid-melamine-based compound salt and/or polyphosphoric acid-diamine compound salt, and (F) an ion scavenger and/or a heavy metal deactivator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an adhesive composition that ishalogen-free, and yields a cured product, upon curing, that exhibitsexcellent flame retardancy and anti-migration properties, and alsorelates to an adhesive sheet, a coverlay film, and a flexiblecopper-clad laminate that use such a composition.

2. Description of the Prior Art

In recent years, developments within the electronics field have beenremarkable, and in particular, communication and consumer electronicdevices have seen considerable progress in terms of deviceminiaturization, weight reduction, and increased component density.Demand for this type of improved performance continues to grow. Inresponse to these demands, flexible printed wiring boards exhibitfavorable flexibility and are resistant to repeated bending, meaningthey can be packaged three dimensionally at a high density within aconfined space. Accordingly, they are being used more and more widely ascomposite components that include functions such as the wiring, cablingor connectors to electronic equipment.

A flexible printed wiring board is produced by forming a circuit on aflexible printed wiring board substrate using normal methods, and thendepending on the intended use of the wiring board, bonding a coverlayfilm to the board to protect the circuit. The flexible printed wiringboard substrate used in the flexible printed wiring board is a laminateprepared by using an adhesive to bond a metal foil to an electricallyinsulating film that exhibits a high level of heat resistance as well asexcellent electrical and mechanical properties. The properties requiredfor the flexible printed wiring board substrate include favorableadhesion durability, as well as favorable levels of heat resistance,flexibility, foldability, anti-migration properties, and flameretardancy. Furthermore, an adhesive sheet refers either to a sheet thatis used for laminating together two or more single-sided copper foil ordouble-sided copper foil flexible printed wiring boards, thereby forminga multilayer structure, or to a sheet that is used for bonding areinforcing sheet to a flexible printed wiring board. The propertiesrequired for such adhesive sheets include favorable adhesive strength,heat resistance, and anti-migration properties.

Against the background of recent environmental problems, there is agrowing trend to limit the use of halogen compounds in componentsmounted within electronic equipment, meaning the use of brominecompounds, which have conventionally been widely used to impart flameretardancy to the materials used for flexible printed wiring boardsubstrates, is becoming increasingly difficult.

As a result of the environmental problems mentioned above, recently, atechnique has been adopted in which a phosphorus-based flame retardantcompound is added to the adhesive instead of a bromine compound in orderto achieve the required flame retardancy. For example, resincompositions have been proposed that comprise an epoxy resin, aphosphate ester compound, a phenol-based curing agent, and an NBR rubberas the primary components (see patent reference 1 and patent reference2). However, phosphate esters exhibit poor resistance to moisture andheat, meaning that under conditions of high temperature and highhumidity, the phosphate ester generates ionic components via hydrolysis,resulting in unsatisfactory levels of anti-migration properties, peelproperties and solvent resistance in the resulting substrate.Furthermore, compositions comprising a phosphazene compound, a polyepoxycompound, a curing agent, a curing accelerator, a synthetic rubber andan inorganic filler have also been proposed (see patent reference 3 andpatent reference 4), but the peel properties, solvent resistance andsolder heat resistance of the resulting substrates are not entirelysatisfactory.

Moreover, research by the inventors of the present invention hasrevealed that even if a composition exhibits excellent anti-migrationproperties within widely used conventional single layer structures, if aplurality of flexible printed wiring board substrates are laminatedtogether to increase the circuit density, or if other heat loading (heathistory) is applied repeatedly, then the resulting anti-migrationproperties may be inadequate. Accordingly, further improvements in theanti-migration properties are required.

[Patent Reference 1] JP 2001-339131A

[Patent Reference 2] JP 2001-339132A

[Patent Reference 3] JP 2001-19930A

[Patent Reference 4] JP 2002-60720A

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide anadhesive composition which, although being halogen-free, exhibitsexcellent flame retardancy, adhesiveness and heat resistance, and notonly exhibits excellent anti-migration properties within widely usedconventional single layer structures, but also exhibits excellentanti-migration properties within multilayer structures of much higherdensity. Another object of the present invention is to provide anadhesive sheet, a coverlay film, and a printed substrate material suchas a copper-clad laminate that use this adhesive composition.

As a result of intensive research aimed at achieving the above objects,the inventors of the present invention discovered that by using aspecific phosphate compound as a flame retardant component, and alsoemploying an ion scavenger and/or a heavy metal deactivator as essentialcomponents, the problems described above could be resolved, and theywere therefore able to complete the present invention.

In other words, the present invention provides a flame retardantadhesive composition comprising:

-   (A) a halogen-free epoxy resin,-   (B) a carboxyl group-containing acrylic resin and/or a carboxyl    group-containing acrylonitrile-butadiene rubber,-   (C) a curing agent,-   (E) a phosphate compound represented by a general formula (1) shown    below and/or a phosphate compound represented by a general    formula (3) shown below:

[wherein, n represents a number from 1 to 100, X₁ represents eitherammonia or a triazine derivative represented by a general formula (2)shown below:

[wherein, Z₁ and Z₂ may be either the same or different, and eachrepresent a group selected from the group consisting of groupsrepresented by a formula: —NR₅R₆ (wherein, R₅ and R₆ may be the same ordifferent, and each represent a hydrogen atom, a straight-chain orbranched alkyl group of 1 to 6 carbon atoms, or a methylol group), ahydroxyl group, a mercapto group, straight-chain or branched alkylgroups of 1 to 10 carbon atoms, straight-chain or branched alkoxy groupsof 1 to 10 carbon atoms, a phenyl group, and a vinyl group], and p is anumber that satisfies: 0<p≦n+2],

[wherein, r represents a number from 1 to 100, Y₁ represents a diaminerepresented by a formula: R₁R₂N(CH₂)_(m)NR₃R₄ (wherein, R₁, R₂, R₃ andR₄ each represent, independently, a hydrogen atom, or a straight-chainor branched alkyl group of 1 to 5 carbon atoms, and m represents aninteger from 1 to 10), piperazine, or a diamine that contains apiperazine ring, and q is a number that satisfies: 0<q≦r+2], and (F) anion scavenger and/or a heavy metal deactivator.

Furthermore, the present invention also provides an adhesive sheethaving a releasable base material, and a layer comprising the aboveadhesive composition formed on one surface of the base material. Thisadhesive sheet is obtained by applying the adhesive composition to abase material having favorable releasability.

Moreover, the present invention also provides a coverlay film, having aninsulating film, and a layer comprising the above composition providedon at least one surface of the insulating film. This coverlay film isobtained by applying the adhesive composition to an insulating film.

Furthermore, the present invention also provides a flexible copper-cladlaminate, having an electrically insulating film, a layer comprising theabove adhesive composition provided on either one surface or bothsurfaces of the insulating film, and either a single copper foil layeror two copper foil layers provided on top of the one or two layers ofthe adhesive composition. This flexible copper-clad laminate is obtainedby using the adhesive composition to bond the electrically insulatingfilm and the copper foil together.

The composition of the present invention yields a cured product, uponcuring, that exhibits excellent flame retardancy, adhesiveness and heatresistance, displays superior anti-migration properties to conventionalproducts, and is also halogen-free. Accordingly, adhesive sheets,coverlay films, and flexible copper-clad laminates prepared using thiscomposition also exhibit excellent flame retardancy, adhesiveness andheat resistance, and even multilayer (laminate) structures that havebeen subjected to repeated heat loading (heat history) exhibit superioranti-migration properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing an outline of thecross-sectional structure of a test specimen used for evaluating theanti-migration properties of a single layer structure.

FIG. 2 is a longitudinal cross-sectional view showing an outline of thecross-sectional structure of a test specimen used for evaluating theanti-migration properties of a multilayer structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Flame Retardant Adhesive Composition>

As follows is a detailed description of the various structuralcomponents of the flame retardant adhesive composition of the presentinvention.

[Halogen-Free Epoxy Resin (A)]

A halogen-free epoxy resin of the component (A) is an epoxy resin thatcontains no halogen atoms such as bromine within the molecularstructure. There are no particular restrictions on this epoxy resin,which may also include silicone, urethane, polyimide, or polyamidestructures or the like. Furthermore, the resin skeleton may also includephosphorus atoms, sulfur atoms, or nitrogen atoms or the like.

Specific examples of this type of epoxy resin include bisphenol A epoxyresins, bisphenol F epoxy resins, and hydrogenated products thereof;glycidyl ether-based epoxy resins such as phenol novolac epoxy resinsand cresol novolac epoxy resins; glycidyl ester-based epoxy resins suchas glycidyl hexahydrophthalate and dimer acid glycidyl ester; glycidylamine-based epoxy resins such as triglycidyl isocyanurate andtetraglycidyldiaminodiphenylmethane; and linear aliphatic epoxy resinssuch as epoxidated polybutadiene and epoxidated soybean oil, and ofthese, bisphenol A epoxy resins, bisphenol F epoxy resins, phenolnovolac epoxy resins, and cresol novolac epoxy resins are preferred.Examples of commercially available products of these resins include thebrand names Epikote 828 (manufactured by Japan Epoxy Resins Co., Ltd.),Epiclon 830S (manufactured by Dainippon Ink and Chemicals,Incorporated), Epikote 517 (manufactured by Japan Epoxy Resins Co.,Ltd.), and EOCN103S (manufactured by Nippon Kayaku Co., Ltd.).

Furthermore, various phosphorus-containing epoxy resins produced bybonding phosphorus atoms to an epoxy resin using a reactive phosphoruscompound can also be used effectively in forming halogen-free flameretardant adhesive compositions. Specific examples of compounds that canbe used include the compounds obtained by reacting an aforementionedepoxy resin with either9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (brand name: HCA,manufactured by Sanko Co., Ltd.), or a compound in which the activehydrogen atom bonded to the phosphorus atom of this compound has beensubstituted with hydroquinone (brand name: HCA-HQ, manufactured by SankoCo., Ltd.). Examples of commercially available products of thesephosphorus-containing epoxy resins include the brand names FX305(manufactured by Tohto Kasei Co., Ltd., phosphorus content: 3% by mass),and Epiclon EXA9710 (manufactured by Dainippon Ink and Chemicals,Incorporated, phosphorus content: 3% by mass). The above epoxy resinsmay be used either alone, or in combinations of two or more differentresins.

[Carboxyl group-containing Acrylic Resin and/or CarboxylGroup-Containing Acrylonitrile-Butadiene Rubber (B)]

Either a carboxyl group-containing acrylic resin and/or a carboxylgroup-containing acrylonitrile-butadiene rubber (hereafter, the term“acrylonitrile-butadiene rubber” is abbreviated as “NBR”) can be used asthe component (B).

Examples of carboxyl group-containing acrylic resins that can be used inthe present invention include resins with a glass transition temperature(Tg) within a range from −40 to 30° C., which contain an acrylate esteras the primary component, and also include a small quantity of acarboxyl group-containing monomer. This glass transition temperature(Tg) is preferably from −10 to 25° C. Provided the glass transitiontemperature is within a range from −40 to 30° C., the adhesive exhibitsan appropriate level of tackiness, and also displays superior handlingproperties. If the glass transition temperature is lower than −40° C.,then the tackiness of the adhesive is excessive, causing a deteriorationin the handling properties. Furthermore, if the glass transitiontemperature exceeds 30° C., then the adhesive lacks adhesiveness. Theglass transition temperature is measured using a differential scanningcalorimeter (DSC).

The weight average molecular weight of the acrylic resin, measured bygel permeation chromatography (GPC, and referenced against polystyrenestandards) is preferably within a range from 100,000 to 1,000,000, andis even more preferably from 300,000 to 850,000.

The acrylic polymer can be prepared using normal solutionpolymerization, emulsion polymerization, suspension polymerization, orbulk polymerization methods, although from the viewpoint of achievingmaximum reduction in the quantity of ionic impurities, which can haveadverse effects on the anti-migration properties, acrylic resinsprepared by suspension polymerization are preferred.

Preferred examples of this acrylic resin include acrylic polymersobtained by copolymerizing three components, namely (a) an acrylateester and/or methacrylate ester, (b) acrylonitrile and/ormethacrylonitrile, and (c) an unsaturated carboxylic acid. This acrylicpolymer may be either a copolymer formed solely from the above threecomponents (a) to (c), or a copolymer that also includes one or moreother components.

(a) (Meth)acrylate Ester

The acrylate ester and/or methacrylate ester of the component (a)imparts flexibility to the acrylic adhesive composition, and specificexamples of suitable (meth)acrylate ester compounds include methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate,isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl(meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, andisodecyl (meth)acrylate. Of these, alkyl (meth)acrylate esters in whichthe alkyl group contains from 1 to 12 carbon atoms, and particularlyfrom 1 to 4 carbon atoms, are preferred. These (meth)acrylate esters ofthe component (a) may be used either alone, or in combinations of two ormore different compounds.

The quantity of the component (a) within the component (A) is preferablywithin a range from 50 to 80% by mass, and even more preferably from 55to 75% by mass. If this quantity is less than 50% by mass, then theadhesive may lose flexibility. In contrast, if the quantity exceeds 80%by mass, then the resulting composition may suffer from exudation duringpress working.

(b) (Meth)acrylonitrile

The acrylonitrile and/or methacrylonitrile of the component (b) impartsheat resistance, adhesiveness and chemical resistance to the adhesivesheet.

The quantity of the component (b) within the component (A) is preferablywithin a range from 15 to 45% by mass, and even more preferably from 20to 40% by mass. If this quantity is less than 15% by mass, then theadhesive may exhibit inferior heat resistance. In contrast, if thequantity exceeds 45% by mass, then the adhesive sheet may loseflexibility.

(c) Unsaturated Carboxylic Acid

The unsaturated carboxylic acid of the component (c) impartsadhesiveness, and also functions as a cross-linking point duringheating. Any copolymerizable vinyl monomer that contains a carboxylgroup may be used, and specific examples of suitable compounds includeacrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acidand itaconic acid.

The quantity of the component (c) within the component (A) is preferablywithin a range from 2 to 10% by mass, and even more preferably from 2 to8% by mass. If this quantity is less than 2% by mass, then thecross-linking effect may be inadequate. In contrast, if the quantityexceeds 10% by mass, then excessive cross-linking within the compositionmay result in poor affinity of the adhesive sheet for the targetadherend, which can cause foaming or blistering during heat curingtreatment or solder bath treatment. Specific examples of this type ofcarboxyl group-containing acrylic resin, listed as commerciallyavailable brand names, include Paracron ME-3500-DR (manufactured byNegami Chemical Industrial Co., Ltd., glass transition temperature: −35°C., weight average molecular weight: 600,000, contains —COOH groups),Teisan Resin WS023DR (manufactured by Nagase ChemteX Corporation, glasstransition temperature: −5° C., weight average molecular weight:450,000, contains —OH/—COOH groups), Teisan Resin SG-280DR (manufacturedby Nagase ChemteX Corporation, glass transition temperature: −30° C.,weight average molecular weight: 900,000, contains —COOH groups), andTeisan Resin SG-708-6DR (manufactured by Nagase ChemteX Corporation,glass transition temperature: 5° C., weight average molecular weight:800,000, contains —OH/—COOH groups). These acrylic resins may be usedeither alone, or in combinations of two or more different resins.

Examples of carboxyl group-containing NBR rubbers that can be used inthe present invention include rubbers produced by carboxylating themolecular chain terminals of a copolymer rubber prepared by acopolymerization of acrylonitrile and butadiene in which the quantity ofacrylonitrile relative to the combined total of acrylonitrile andbutadiene is preferably within a range from 5 to 70% by mass, and evenmore preferably from 10 to 50% by mass, and copolymer rubbers producedby a copolymerization of acrylonitrile, butadiene, and a carboxylgroup-containing monomer such as acrylic acid or maleic acid. The abovecarboxylation can be conducted using a monomer that contains a carboxylgroup, such as methacrylic acid.

There are no particular restrictions on the proportion of carboxylgroups within the carboxyl group-containing NBR (in other words, theratio of the above monomer that contains a carboxyl group relative tothe combined total of all the monomers that constitute the carboxylgroup-containing NBR), but this proportion is preferably within a rangefrom 1 to 10 mol %, and is even more preferably from 2 to 6 mol %.Provided this proportion satisfies this range from 1 to 10 mol %, thefluidity of the product composition can be controlled, meaning afavorable level of curability can be achieved.

Specific examples of these carboxyl group-containing NBR rubbers, listedin terms of their brand names, include Nipol 1072 (manufactured by ZeonCorporation), and the high-purity, low ionic impurity product PNR-1H(manufactured by JSR Corporation). High-purity carboxyl group-containingacrylonitrile butadiene rubbers are very expensive and can therefore notbe used in large quantities, although they are effective insimultaneously improving the adhesion and the anti-migration properties.

There are no particular restrictions on the blend quantity of thecomponent (B), although the quantity is typically within a range from 10to 200 parts by mass, and preferably from 20 to 150 parts by mass, per100 parts by mass of the component (A). Provided the quantity of thecomponent (B) falls within this range from 10 to 200 parts by mass, theproduced flexible copper-clad laminate, coverlay film, and adhesivesheet exhibit superior flame retardancy, and superior peel strength fromthe copper foil.

The above carboxyl group-containing acrylic resin and/or the carboxylgroup-containing NBR can each be used either alone, or in combinationsof two or more different materials.

[Curing Agent (C)]

There are no particular restrictions on the curing agent of thecomponent (C), and any of the materials typically used as epoxy resincuring agents can be used. Examples of the curing agent includepolyamine-based curing agents, acid anhydride-based curing agents, borontrifluoride amine complex salts, and phenol resins. Specific examples ofpolyamine-based curing agents include aliphatic amine-based curingagents such as diethylenetriamine, tetraethylenetetramine andtetraethylenepentamine, alicyclic amine-based curing agents such asisophorone diamine, aromatic amine-based curing agents such asdiaminodiphenylmethane and phenylenediamine, and dicyandiamide. Specificexamples of acid anhydride-based curing agents include phthalicanhydride, pyromellitic anhydride, trimellitic anhydride, andhexahydrophthalic anhydride. Of these, from the viewpoint of ensuring asuitable level of reactivity when the product composition is used in acoverlay film, polyamine-based curing agents are preferred, whereas fromthe viewpoint of imparting a superior level of heat resistance when theproduct composition is used in a flexible copper-clad laminate, acidanhydride-based curing agents are preferred. The curing agent of thecomponent (C) may be used either alone, or in a combination of two ormore different compounds.

There are no particular restrictions on the blend quantity of thecomponent (C), although the quantity is typically within a range from0.5 to 20 parts by mass, and preferably from 1 to 15 parts by mass, per100 parts by mass of the component (A).

[Curing Accelerator (D)]

In the present invention, the component (D) is not an essentialcomponent, but is preferably added to the composition. There are noparticular restrictions on the curing accelerator of the component (D),provided it accelerates the reaction between the halogen-free epoxyresin (A) and the curing agent (C), and contains no halogen atoms.Specific examples of this curing accelerator include imidazole compoundssuch as 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole,ethyl isocyanate compounds of these compounds, 2-phenylimidazole,2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole,and 2-phenyl-4,5-dihydroxymethylimidazole; triorganophosphine compoundssuch as triphenylphosphine, tributylphosphine,tris(p-methylphenyl)phosphine, tris(p-methoxyphenyl)phosphine,tris(p-ethoxyphenyl)phosphine, triphenylphosphine-triphenylborate, andtetraphenylphosphine-tetraphenylborate; quaternary phosphonium salts;tertiary amines such as triethyleneammonium triphenylborate, and thetetraphenylborate thereof; and octylate salts such as tin octylate andzinc octylate. These curing accelerators may be used either alone, or incombinations of two or more different compounds.

There are no particular restrictions on the blend quantity of thecomponent (D), although the quantity is typically within a range from0.1 to 15 parts by mass, preferably from 0.5 to 10 parts by mass, andeven more preferably from 1 to 5 parts by mass, per 100 parts by mass ofthe component (A).

[Phosphate Compound (E) Represented by the General Formula (1) or theGeneral Formula (3)]

The phosphate compounds of the component (E) represented by the abovegeneral formula (1) or the above general formula (3) contain no halogenatoms, and are used for imparting flame retardancy to the composition.

Specific examples of the above phosphate compounds include salts ofpolyphosphoric acid and melamine, and salts of polyphosphoric acid andpiperazine. Furthermore, examples of the polyphosphoric acid includepyrophosphoric acid, tripolyphosphoric acid, and pentapolyphosphoricacid. Of the above phosphate compounds, the use of a melamine salt ofpyrophosphoric acid and/or a piperazine salt of pyrophosphoric acid ispreferred. Because the above phosphate compounds include phosphorusatoms and nitrogen atoms within their molecular structure, they yieldparticularly high levels of flame retardancy. Moreover, the abovephosphate compounds have a high phosphorus content. Furthermore, theabove phosphate compounds are insoluble in the organic solvents such asmethyl ethyl ketone, toluene and dimethylacetamide typically used inadhesive varnishes, and are also insoluble in epoxy resin components,meaning that when used within a coverlay film, these compounds offer theadvantage of being resistant to exudation during heat press curing ofthe coverlay film.

The average particle size of the above phosphate compound used in thepresent invention is typically not more than 20 μm, and is preferablynot more than 10 μm. If the average particle size of the phosphatecompound exceeds 20 μm, then the dispersibility of the compound withinthe composition of the present invention deteriorates, which can lead toproblems in terms of the flame retardancy, heat resistance and theinsulating properties. An example of a commercially available product ofthe above phosphate compound is the product Adeka STAB FP-2100(manufactured by Asahi Denka Co., Ltd., a mixture of melaminepyrophosphate and piperazine pyrophosphate, phosphorus content: 18 to21% by mass).

Other phosphorus-based flame retardants may also be used in combinationwith the above phosphate compound, provided addition of these otherretardants does not impair the anti-migration properties. However, thephosphate compound is preferably used alone, and the combined use ofphosphate esters is particularly undesirable, as these esters cause asignificant deterioration in the anti-migration properties.

There are no particular restrictions on the blend quantity of thecomponent (E), although in order to ensure a favorable level of flameretardancy, the phosphorus content, relative to the organic resincomponents within the adhesive composition (excluding the inorganicsolid components), is preferably within a range from 2.0 to 4.0% bymass, and is even more preferably from 2.5 to 3.5% by mass. If thisratio is less than 2.0% by mass, then ensuring the desired level offlame retardancy within the adhesive composition is difficult, whereasif the ratio exceeds 4.0% by mass, the heat resistance of the adhesivecomposition tends to worsen.

[Ion Scavenger and/or Heavy Metal Deactivator (F)]

The ion scavenger and/or heavy metal deactivator of the component (F)further improves the anti-migration properties.

An ion scavenger refers to a compound with an ion trapping function, andis used to reduce the quantity of ionic impurities by trapping phosphateanions, organic acid anions, halogen anions, alkali metal cations,alkaline earth metal cations and the like. If the composition contains alarge quantity of ionic impurities, then wire corrosion can become aproblem, and the anti-migration properties of the insulating layerdeteriorate markedly. Specific examples of this type of ion scavengerinclude hydrotalcite-based ion scavengers, bismuth oxide-based ionscavengers, antimony oxide-based ion scavengers, titaniumphosphate-based ion scavengers, and zirconium phosphate-based ionscavengers. Examples of suitable commercially available ion scavengersinclude the products DHT-4A (a hydrotalcite-based ion scavenger,manufactured by Kyowa Chemical Industry Co., Ltd.), IXE-100 (a zirconiumphosphate-based ion scavenger, manufactured by Toagosei Co., Ltd.),IXE-300 (an antimony oxide-based ion scavenger, manufactured by ToagoseiCo., Ltd.), IXE-400 (a titanium phosphate-based ion scavenger,manufactured by Toagosei Co., Ltd.), IXE-500 (a bismuth oxide-based ionscavenger, manufactured by Toagosei Co., Ltd.), and IXE-600 (an antimonyoxide-bismuth oxide-based ion scavenger, manufactured by Toagosei Co.,Ltd.).

Furthermore, the heavy metal deactivator inhibits the elution of copperions and improves the anti-migration properties by deactivating thesurface of the copper wiring of the flexible printed wiring board.Specific examples of this type of heavy metal deactivator includenitrogen compounds such as hydrazides and triazoles. Examples ofsuitable commercially available heavy metal deactivators include IrganoxMD1024 (a hydrazide-based heavy metal deactivator, manufactured by CibaSpecialty Chemicals Inc.) and BT-120 (a benzotriazole-based heavy metaldeactivator, manufactured by Johoku Chemical Co., Ltd.).

The ion scavengers and heavy metal deactivators described above may beused either alone, or in combinations of two or more differentmaterials.

There are no particular restrictions on the blend quantity of thecomponent (F), although the quantity is typically within a range from0.1 to 5 parts by mass, and preferably from 0.5 to 3 parts by mass, per100 parts by mass of the component (A).

[Other Optional Components]

In addition to the components (A) through (F) described above, otheroptional components may also be added, provided they do not impair theobjects or effects of the present invention.

Inorganic Fillers

Inorganic fillers other than the phosphate compound of the component (E)may be added. There are no particular restrictions on these inorganicfillers, and any fillers used in conventional adhesive sheets, coverlayfilms, and flexible copper-clad laminates can be used. Specifically,from the viewpoint of also functioning as a flame retardancy assistant,metal oxides such as aluminum hydroxide, magnesium hydroxide, silicondioxide and molybdenum oxide can be used, and of these, aluminumhydroxide and magnesium hydroxide are preferred. These inorganic fillersmay be used either alone, or in combinations of two or more differentcompounds. There are no particular restrictions on the blend quantity ofthe above inorganic filler, although the quantity is preferably within arange from 5 to 50 parts by mass, and even more preferably from 10 to 40parts by mass, per 100 parts by mass of the combination of the organicresin components within the adhesive composition.

Organic Solvents

The components (A) to (F) described above, and any optional componentsthat are added as required, may be used in a solventless form in theproduction of flexible copper-clad laminates, coverlay films andadhesive sheets, or may be dissolved or dispersed in an organic solventto form a solution or dispersion of the composition (hereafter simplyreferred to as a “solution”). Examples of suitable organic solventsinclude N,N-dimethylacetamide, methyl ethyl ketone,N,N-dimethylformamide, cyclohexanone, N-methyl-2-pyrrolidone, toluene,methanol, ethanol, isopropanol and acetone. Of these,N,N-dimethylacetamide, methyl ethyl ketone, N,N-dimethylformamide,cyclohexanone, N-methyl-2-pyrrolidone and toluene are preferred, andN,N-dimethylacetamide, methyl ethyl ketone and toluene are particularlypreferred. These organic solvents may be used either alone, or incombinations of two or more different solvents.

The combined concentration of the organic resin components and theinorganic solid components within the above adhesive solution istypically within a range from 10 to 45% by mass, and is preferably from20 to 40% by mass. Provided this concentration falls within this rangefrom 10 to 45% by mass, the adhesive solution exhibits favorable ease ofapplication to substrates such as electrically insulating films, thusproviding superior workability. Moreover, the adhesive solution alsooffers superior coating properties, with no irregularities occurringduring coating, while also providing superior performance in terms ofenvironmental and economic factors.

The term “organic resin components” refers to the non-volatile organiccomponents that constitute the cured product obtained by curing theadhesive composition of the present invention. Specifically, the organicresin components include mainly the halogen-free epoxy resin (A), thecarboxyl group-containing acrylic resin and/or carboxyl group-containingacrylonitrile-butadiene rubber (B), the curing agent (C), the curingaccelerator (D), the phosphate compound (E) represented by the generalformula (1) or the general formula (3), the heavy metal deactivator (F),and any other optional organic components. In those cases where theadhesive composition includes an organic solvent, the organic solvent isnot usually included 95 within these organic resin components.Furthermore, the term “inorganic solid components” refers to thenon-volatile inorganic solid components included within the adhesivecomposition of the present invention, and specific examples include theion scavenger (F), and any inorganic fillers that may be optionallyadded.

The organic resin components within the composition of the presentinvention, together with optionally added inorganic solid components andorganic solvents, can be mixed together using a pot mill, ball mill,homogenizer, super mill or the like.

<Coverlay Films>

The composition described above can be used in the production ofcoverlay films. Specifically, coverlay films having an electricallyinsulating film, and a layer comprising the above adhesive compositionprovided on at least one surface of the film can be produced. Thecoverlay film may also include an optional protective layer, which isprovided on top of the layer of the adhesive composition in order toprotect the adhesive composition layer. Furthermore, in those caseswhere the electrically insulating film is very thin, a support layer maybe bonded to the electrically insulating film to reinforce the film.

As follows is a description of a process for producing such a coverlayfilm.

An adhesive solution prepared in a liquid form by mixing the requiredcomponents with an organic solvent is applied to an electricallyinsulating film using a reverse roll coater, a comma coater or the like.The electrically insulating film with the applied adhesive solution isthen passed through an in-line dryer, and heated at 80 to 160° C. for aperiod of 2 to 10 minutes, thereby removing the organic solvent anddrying the adhesive composition to form a semi-cured state. A rolllaminator is then used to crimp and laminate the semi-cured layer of theadhesive composition to a releasable base material that functions as aprotective layer, thereby forming a coverlay film. The releasable basematerial is peeled off at the time of use. The term “semi-cured state”refers to a state where the composition is dry, and the curing reactionhas begun within portions of the composition.

The dried thickness of the adhesive composition layer in the abovecoverlay film is typically within a range from 5 to 45 μm, and ispreferably from 5 to 35 μm.

Electrically Insulating Film

The above electrically insulating film is also used in flexiblecopper-clad laminates of the present invention. There are no particularrestrictions on the electrically insulating film, and any film that istypically used in flexible copper-clad laminates or coverlay films canbe used. Specific examples of suitable electrically insulating filmsinclude polyimide films, aramid films, polyethylene terephthalate films,polyethylene naphthalate films, polyester films, polyparabanic acidfilms, polyether etherketone films and polyphenylene sulfide films aswell as films produced by impregnating a base comprising glass fiber,aramid fiber, polyester fiber or the like with a matrix such as an epoxyresin or acrylic resin, subsequently forming the impregnated base into afilm or sheet form, and then bonding the film or sheet to copper foil.From the viewpoints of achieving favorable heat resistance, dimensionalstability and mechanical properties for the produced coverlay film, theuse of low temperature plasma-treated polyimide films or corona-treatedaramid films is particularly desirable. Any of the polyimide filmstypically used in coverlay films can be used. The thickness of thiselectrically insulating film can be set to any desired value dependingon need, although thickness values from 9 to 50 μm are preferred.Furthermore, any of the aramid films typically used in coverlay filmscan be used, and although the thickness of this aramid film can be setto any desired value depending on need, thickness values from 3 to 9 μmare preferred. Aramid films generally have a higher modulus ofelongation than polyimide films, and consequently exhibit superiorhandling properties even for very thin films. However, in those caseswhere handling of a thin film is difficult, the handling properties canbe improved by bonding a support film such as a polyethyleneterephthalate film that has been coated with an adhesive to the thinfilm.

Accordingly, in a representative example of a coverlay film in which anaramid film is used as the electrically insulating film, the coverlayfilm comprises an electrically insulating film comprising a support filmand an aramid film with a thickness of 3 to 9 μm supported on thesupport film, a layer comprising the above adhesive composition providedon at least one surface of the insulating film, and a releasable basematerial provided on top of the adhesive composition layer.

Releasable Base Material (Protective Layer)

There are no particular restrictions on the releasable base materialdescribed above, provided it is a film material that protects theadhesive composition layer, and if required, is able to be peeled offfrom the adhesive composition layer without damaging the state of theadhesive layer. Examples of suitable films include plastic films such aspolyethylene (PE) films, polypropylene (PP) films, polymethylpentene(TPX) films, and release-treated polyester films; and release sheets inwhich a polyolefin film such as a PE film or PP film, a TPX film, or arelease-treated polyester film is coated onto one side or both sides ofa paper material. There are no particular restrictions on the thicknessof the releasable base material, although typical thickness values arewithin a range from approximately 25 to 150 μm.

<Adhesive Sheets>

The adhesive composition described above can be used in the productionof adhesive sheets. Specifically, adhesive sheets having a layercomprising the above composition, and a releasable base material thatfunctions as a protective layer, which covers the layer comprising thecomposition and is provided on at least one surface of the adhesivelayer, can be produced. This releasable base material can use the samematerials as those described above in the section relating to theprotective layer for a coverlay film. The dried thickness of theadhesive layer in the above adhesive sheets is typically within a rangefrom approximately 5 to 50 μm, and is preferably from approximately 10to 40 μm. The thickness of the releasable base material layer istypically within a range from approximately 25 to 150 μm, and ispreferably from approximately 30 to 140 μm.

As follows is a description of a process for producing an adhesive sheetof the present invention.

An adhesive composition of the present invention, prepared in a solutionform by mixing the required components with an organic solvent, isapplied to a releasable base material using a reverse roll coater, acomma coater or the like. The releasable base material with the appliedadhesive solution is then passed through an in-line dryer, and heated at80 to 160° C. for a period of 2 to 10 minutes, thereby removing theorganic solvent and drying the adhesive composition to form a semi-curedstate. A roll laminator is then used to crimp and laminate thesemi-cured adhesive composition layer to another releasable basematerial, thereby forming an adhesive sheet.

<Flexible Copper-clad Laminates>

The composition of the present invention can be used in the productionof flexible copper-clad laminates. Specifically, flexible copper-cladlaminates having an electrically insulating film, a layer comprising theabove adhesive composition provided on either one surface or bothsurfaces of the film, and one or two layers of copper foil bonded to theone or two layers of the composition can be produced. The electricallyinsulating film can use the same electrically insulating films as thosedescribed above in the section relating to coverlay films. As follows isa description of a process for producing a flexible copper-cladlaminate.

An adhesive composition of the present invention, prepared in a solutionform by mixing the required components with an organic solvent, isapplied to an electrically insulating film using a reverse roll coater,a comma coater or the like. The electrically insulating film with theapplied adhesive solution is then passed through an in-line dryer, andheated at 80 to 160° C. for a period of 2 to 10 minutes, therebyremoving the organic solvent and drying the composition to form asemi-cured state. A copper foil is then placed on top of the semi-curedadhesive composition layer, and heat lamination (thermocompressionbonding) at a temperature from 100 to 150° C. is used to form alaminate. By subjecting this laminate to post-curing at 80 to 160° C.,the semi-cured composition is completely cured, yielding the finalflexible copper-clad laminate.

The dried thickness of the adhesive composition layer in the aboveflexible copper-clad laminate is typically within a range from 5 to 45μm, and is preferably from 5 to 18 μm.

The copper foil described above can use the rolled copper foil orelectrolytic copper foil typically used in conventional flexiblecopper-clad laminates. The thickness of this copper foil is typicallywithin a range from 3 to 70 μm.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples, although the present invention is in no waylimited by the examples presented below. The components (A) through (F),and the other optional components used in the examples are as specifiedbelow. The units for the numbers representing the blend proportions inthe tables are “parts by mass”.

<Adhesive Composition Components>

(A) Halogen-Free Epoxy Resin

-   (1) Epikote 828 (brand name) (manufactured by Japan Epoxy Resins    Co., Ltd., epoxy equivalent weight: 184 to 194)-   (2) Epikote 1001 (brand name) (manufactured by Japan Epoxy Resins    Co., Ltd., epoxy equivalent weight: 450 to 500)-   (3) EOCN-103S (brand name) (manufactured by Nippon Kayaku Co., Ltd.,    epoxy equivalent weight: 209 to 219)-   (4) NC-3000-H (brand name) (manufactured by Nippon Kayaku Co., Ltd.,    epoxy equivalent weight: 280 to 300)-   (5) EP-49-20 (brand name) (manufactured by Asahi Denka Co., Ltd.,    epoxy equivalent weight: 200)

(B) Carboxyl group-containing Acrylic Resin and/or CarboxylGroup-Containing Acrylonitrile-butadiene Rubber

-   (1) Nipol 1072 (brand name) (a carboxyl group-containing NBR,    manufactured by Zeon Corporation)-   (2) Teisan Resin SG-708-6DR (brand name) (a carboxyl    group-containing acrylic resin, manufactured by Nagase ChemteX    Corporation)

(C) Curing Agents

-   (1) 4,4′-diaminodiphenylsulfone (DDS, a diamine-based curing agent)-   (2) Phenolite TD-2093 (brand name) (a novolac-type phenol resin,    manufactured by Dainippon Ink and Chemicals Inc., OH equivalent    weight: 104)

(D) Curing Accelerator

-   (1) 2E4MZ (brand name) (an imidazole-based curing accelerator,    manufactured by Shikoku Chemical Corporation)

(E) Phosphate Compound

-   (1) Adeka STAB FP-2100 (brand name) (a phosphate compound,    manufactured by Asahi Denka Co., Ltd., phosphorus content: 18 to 21%    by mass)

(F) Ion Scavenger, Heavy Metal Deactivator

-   (1) DHT-4A (brand name) (a magnesium-aluminum    hydroxide-carbonate-hydrate (Mg_(4.3)Al₂(OH)_(12.6)CO₃.mH₂O), an ion    scavenger manufactured by Kyowa Chemical Industry Co. Ltd.)-   (2) BT-120 (brand name) (1,2,3-benzotriazole, a heavy metal    deactivator manufactured by Johoku Chemical Co., Ltd.).

Inorganic Filler

-   (1) Aluminum Hydroxide    -   Other Phosphorus-Based Flame Retardants-   PX-200 (brand name) (an aromatic condensed phosphate ester,    manufactured by Daihachi Chemical Industry Co., Ltd., phosphorus    content: 9.0% by mass)-   SP-703 (brand name) (an aromatic phosphate esteramide, manufactured    by Shikoku Chemical Corporation, phosphorus content: 10% by mass)-   SPE-100 (brand name) (phosphazene, manufactured by Otsuka Chemical    Co., Ltd., phosphorus content: 13% by mass)<    <Properties of Flexible Copper-Clad Laminates and Coverlay Films>

Example 1

Preparation of Adhesive Composition

Each of the adhesive composition components were combined in theproportions shown in the column labeled “blend example 1” in Table 1,and a mixed solvent of methyl ethyl ketone and toluene with a mass ratioof 1/1 was then added to the resulting mixture, yielding a dispersion inwhich the combined concentration of the organic solid components and theinorganic solid components was 35% by mass.

Preparation of Flexible Copper-Clad Laminate

The above dispersion was then applied to the surface of a polyimide filmA (brand name: Kapton, manufactured by DuPont Toray Co., Ltd.,thickness: 25 μm) using an applicator, in sufficient quantity togenerate a dried coating of the composition with a thickness of 18 μm,and the applied coating was then dried for 10 minutes at 120° C. in aforced air oven, thereby converting the composition to a semi-curedstate. The dispersion-coated surface of the polyimide film A and aroughened surface of a rolled copper foil (manufactured by Nippon Mining& Metals Co., Ltd., thickness: 18 μm) were then bonded together bythermocompression bonding using a roll laminator at 120° C. and a linearpressure of 20 N/cm, and the resulting laminate was then subjected topost-curing for one hour at 80° C., and a further 4 hours at 160° C.,thereby completing the preparation of a flexible copper-clad laminate.

Preparation of Coverlay Film

The above dispersion was applied to the surface of a polyimide film A(brand name: Kapton, manufactured by DuPont Toray Co., Ltd., thickness:25 μm) using an applicator, in sufficient quantity to generate a driedcoating of the composition with a thickness of 25 μm, and the appliedcoating was then dried for 10 minutes at 120° C. in a forced air oven,thereby converting the composition to a semi-cured state, and completingpreparation of a coverlay film.

Example 2

With the exception of combining the adhesive composition components inthe proportions shown in the column labeled “blend example 2” in Table1, a flexible copper-clad laminate and a coverlay film were prepared inthe same manner as the example 1.

Example 3

With the exception of combining the adhesive composition components inthe proportions shown in the column labeled “blend example 3” in Table1, a flexible copper-clad laminate and a coverlay film were prepared inthe same manner as the example 1.

Example 4

Preparation of Flexible Copper-Clad Laminate

A mixture produced by combining each of the adhesive compositioncomponents in the proportions shown in the column labeled “blend example1” in Table 1 was applied to the surface of an aramid film (brand name:Aramica, manufactured by Teijin Advanced Film Co., Ltd., thickness: 4μm) using an applicator, in sufficient quantity to generate a driedcoating of the composition with a thickness of 10 μm, and the appliedcoating was then dried for 10 minutes at 120° C. in a forced air oven,thereby converting the composition to a semi-cured state. Thedispersion-coated surface of the aramid film and a roughened surface ofan electrolytic copper foil (manufactured by Mitsui Mining & SmeltingCo., Ltd., thickness: 9 μm) were then bonded together bythermocompression bonding using a roll laminator at 120° C. and a linearpressure of 20 N/cm, and the resulting laminate was then subjected topost-curing for one hour at 80° C., and a further 4 hours at 160° C.,thereby completing the preparation of a flexible copper-clad laminate.

Preparation of Coverlay Film

The above adhesive solution was applied to the surface of an aramid film(brand name: Aramica, manufactured by Teijin Advanced Film Co., Ltd.,thickness: 4 μm) using an applicator, in sufficient quantity to generatea dried coating of the composition with a thickness of 10 μm, and theapplied coating was then dried for 10 minutes at 120° C. in a forced airoven, thereby converting the composition to a semi-cured state, andcompleting preparation of a coverlay film.

Comparative Examples 1 to 9

With the exception of combining the adhesive composition components inthe proportions shown in the columns labeled comparative blend examples1 to 9 in Table 1, flexible copper-clad laminates and coverlay filmswere prepared in the same manner as the example 4.

Comparative Example 10

With the exception of combining the adhesive composition components inthe proportions shown in the column labeled “comparative blend example2” in Table 1, a flexible copper-clad laminate and a coverlay film wereprepared in the same manner as the example 3.

[Measurements]

The properties of the flexible copper-clad laminates prepared in theexamples 1 to 4 and the comparative examples 1 to 10 were measured inaccordance with the measurement methods 1 described below. Theproperties of the prepared coverlay films were measured in accordancewith the measurement methods 2 described below. Furthermore, theanti-migration properties of the flexible copper-clad laminates and thecoverlay films were measured in accordance with the measurement method 3described below. The results of the measurements are shown in Table 2.

—Measurement Methods 1 —

1-1. Peel Strength

The peel strength was measured in accordance with JIS C6471, by forminga circuit with a pattern width of 1 mm on the flexible copper-cladlaminate, and then measuring the minimum value for the force required topeel the copper foil (the circuit) at a speed of 50 mm/minute in adirection at an angle of 90 degrees to the surface of the laminate underconditions at 25° C. This measured value was reported as the peelstrength. However, for those laminates in which an aramid film was usedas the electrically insulating film (the example 4 and the comparativeexample 10), the minimum value for the force required to peel the copperfoil at a speed of 50 mm/minute in a direction at an angle of 180degrees to the surface of the laminate was measured and reported as thepeel strength.

1-2. Solder Heat Resistance (Normal Conditions, Moisture Absorption)

Normal conditions: The solder heat resistance was measured in accordancewith JIS C6471, by preparing test specimens by cutting the flexiblecopper-clad laminate into 25 mm squares, and then floating these testspecimens for 30 seconds on a 300° C. solder bath. If the test specimensexhibited no blistering, peeling or discoloration, then the solder heatresistance was evaluated as “good”, and was recorded using the symbol ◯,whereas if the test specimens exhibited at least one of blistering,peeling and discoloration, then the solder heat resistance was evaluatedas “poor”, and was recorded using the symbol x.

Moisture absorption: Test specimens prepared in the same manner as thoseprepared for the aforementioned measurement of the solder heatresistance under normal conditions were left to stand for 24 hours in anatmosphere at a temperature of 40° C. and a relative humidity of 90%,and the test specimens were then floated for 30 seconds on a 260° C.solder bath. If the test specimens exhibited no blistering, peeling ordiscoloration, then the solder heat resistance was evaluated as “good”,and was recorded using the symbol ◯, whereas if the test specimensexhibited at least one of blistering, peeling and discoloration, thenthe solder heat resistance was evaluated as “poor”, and was recordedusing the symbol x.

1-3. Flame Retardancy

A sample was first prepared by removing the entire copper foil from theflexible copper-clad laminate using an etching treatment. The flameretardancy of this sample was then measured in accordance with the flameretardancy standard UL94VTM-0. If the sample satisfied the UL94VTM-0standard it was evaluated as “good”, and was recorded using the symbol◯, whereas if the sample did not satisfy the UL94VTM-0 standard, it wasevaluated as “poor”, and was recorded using the symbol x.

—Measurement Methods 2 —

2-1. Peel Strength

The peel strength was measured in accordance with JIS C6471, by firstpreparing a pressed sample by bonding the adhesive layer of the coverlayfilm to the glossy surface of a rolled copper foil (manufactured byNippon Mining & Metals Co., Ltd., thickness: 18 μm) using a press device(temperature: 160° C., pressure: 3 MPa, time: 30 minutes). The preparedpressed sample was then cut to form a test specimen with a width of 1 cmand a length of 15 cm. The surface of the electrically insulating filmof this test specimen was secured (in the case of an aramid film, thefilm is very thin and prone to rupture, and is consequently reinforcedby bonding a mending tape to the rear surface of the film), and theminimum value for the force required to peel the copper foil at a speedof 50 mm/minute in a direction at an angle of 90 degrees to the surfaceof the electrically insulating film under conditions at 25° C. was thenmeasured, and this measured value was reported as the peel strength.

2-2. Solder Heat Resistance (Normal Conditions, Moisture Absorption)

With the exception of preparing the test specimens by cutting 25 mmsquare samples from a pressed sample of the coverlay film, which wasprepared in the same manner as that described above for the measurementof the peel strength, the solder heat resistance was measured undernormal conditions and under conditions of moisture absorption in thesame manner as that described in the above measurement method 1-2.

2-3. Flame Retardancy

A sample was first prepared by removing the entire copper foil from anaforementioned pressed sample using an etching treatment. The flameretardancy of this sample was then measured in accordance with the flameretardancy standard UL94VTM-0. If the sample satisfied the UL94VTM-0standard it was evaluated as “good”, and was recorded using the symbol◯, whereas if the sample did not satisfy the UL94VTM-0 standard, it wasevaluated as “poor”, and was recorded using the symbol x.

—Measurement Methods 3 —

3-1. Anti-Migration Properties (Evaluation of Single Layer Structuresand Multilayer Structures)

Using the flexible copper-clad laminates and coverlay films from each ofthe examples, as well as adhesive sheets having an adhesive compositionlayer (25 μm) on one surface of a polyester film, prepared in the samemanner as the example 5 described below but with the exception of usingthe adhesive dispersions from each of the examples, test specimens witha single layer structure and test specimens with a multilayer structurewere prepared. A more detailed description is provided below.

Test Specimen for Evaluating Single Layer Structure

A test specimen for evaluating a single layer structure with thecross-sectional structure shown in FIG. 1 was prepared. A comb-shapedcircuit in which the ratio of line width/space width=80 μm/80 μm wasformed on the flexible copper-clad laminate, and the coverlay film wasthen bonded to the circuit-bearing surface using a press device, underconditions including a temperature of 160° C., a pressure of 3 MPa and acompression time of 30 minutes, thereby forming a test specimen forevaluating a single layer structure. In FIG. 1, numeral 1 represents anelectrically insulating film originating from the coverlay film, numeral2 represents an adhesive layer originating from the coverlay film,numeral 3 represents an adhesive layer originating from the flexiblecopper-clad laminate, numeral 4 represents an electrically insulatingfilm originating from the flexible copper-clad laminate, and numeral 5represents a conductor (the copper circuit).

Test Specimen for Evaluating Multilayer Structure

A test specimen for evaluating a multilayer structure with thecross-sectional structure shown in FIG. 2 was prepared. The adhesivelayers of two separate adhesive sheets were bonded to the upper andlower surfaces respectively of a single layer evaluation test specimenprepared in the manner described above, and the polyester films thatfunction as the protective layers were then peeled off from the adhesivesheets to expose the underlying adhesive layers. Two glass epoxy sheets(thickness: 1 mm) were then bonded to the adhesive layers provided onthe upper and lower surfaces of the single layer evaluation testspecimen, thereby sandwiching the test specimen between the two glassepoxy sheets, and thermocompression bonding was then conducted for 30minutes under conditions including a temperature of 160° C. and apressure of 3 MPa, thus forming a test specimen for evaluating amultilayer structure. In FIG. 2, numerals 1 to 5 are as defined for FIG.1, numeral 6 represents an adhesive layer originating from an adhesivesheet, and numeral 7 represents a glass epoxy sheet.

Under conditions including a temperature of 85° C. and a relativehumidity of 85%, the anti-migration properties of each of the preparedtest specimens was measured by applying a direct current voltage of 50 Vacross the terminals of the test specimen (using a migration testerMIG-86, manufactured by IMV Corporation).

The voltage was applied for 1,000 hours, and those specimens in which ashort circuit occurred (indicated by a reduction in the resistance)within the conductor 5 prior to the completion of the 1,000 hours, andthose specimens in which dendrite growth was detected after 1,000 hourswere evaluated as “poor” and were recorded using the symbol x, whereasthose specimens for which the resistance value was maintained even after1,000 hours, and in which no dendrites were detected were evaluated as“good”, and were recorded using the symbol ◯.

TABLE 1 Blend Example Comparative Blend Example Component 1 2 3 1 2 3 AHalogen-free epoxy resin Epikote 828 40 40 40 40 40 Epikote 1001 25EOCN-103S 40 25 40 40 40 40 NC-3000-H 50 EP-49-20 20 20 20 20 20 B NBRNipol 1072 40 20 Acrylic resin SG-708-6DR 100 40 100 100 100 C Curingagent DDS 10 10 10 10 10 TD-2093 10 D Curing accelerator 2E4MZ 1 1 1 1 11 E Phosphate Compound FP-2100 40 30 35 40 F Ion scavenger DHT-4A 1 1 11 Heavy metal deactivator BT-120 1 Optional component: Inorganic fillerAluminum hydroxide 20 25 20 20 20 20 Other Phosphate ester PX-200 40 85Phosphate esteramide SP-703 Phosphazene SPE-100 Phosphorus contentwithin adhesive composition (%) 3.1% 3.2% 3.3% 3.1% 1.4% 2.6% (excludinginorganic solid components) Comparative Blend Example Component 4 5 6 78 9 A Halogen-free epoxy resin Epikote 828 40 40 40 40 Epikote 1001 2525 EOCN-103S 40 40 40 40 25 25 NC-3000-H 50 50 EP-49-20 20 20 20 20 BNBR Nipol 1072 40 40 Acrylic resin SG-708-6DR 100 100 100 100 C Curingagent DDS 10 10 10 10 TD-2093 10 10 D Curing accelerator 2E4MZ 1 1 1 1 11 E Phosphate Compound FP-2100 F Ion scavenger DHT-4A 1 1 1 Heavy metaldeactivator BT-120 1 1 Optional component: Inorganic filler Aluminumhydroxide 20 20 20 20 25 25 Other Phosphate ester PX-200 85 30 60Phosphate esteramide SP-703 75 Phosphazene SPE-100 40 60 Phosphoruscontent within adhesive composition (%) 2.6% 2.6% 2.1% 2.9% 1.5% 2.5%(excluding inorganic solid components)

TABLE 2 Example Comparative Example Measurement Item 1 2 3 4 1 2 3 4 5Adhesive composition Blend Blend Blend Blend Compara- Compara- Compara-Compara- Compara- example 1 example 2 example 3 example 1 tive tive tivetive tive blend blend blend blend blend example 1 example 2 example 3example 4 example 5 Electrically insulating film PI PI PI AR PI PI PI PIPI (Polyimide: PI, aramid: AR) Evaluation of copper-clad laminate Peelstrength (N/cm) 12.5 9.5 9.0 8.8 12.5 5.0 4.2 4.2 6.1 Solder heatresistance (° C.) Normal conditions 300° C. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Moistureabsorption 260° C. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ x Flame retardancy (UL94, VTM-0) ∘ ∘∘ ∘ ∘ x ∘ ∘ ∘ Anti-migration properties Evaluation of single layerstructure ∘ ∘ ∘ ∘ ∘ x x x x Evaluation of multilayer structure ∘ ∘ ∘ ∘ xx x x x Evaluation of coverlay film Peel strength (N/cm) 9.5 9.3 8.7 8.59.5 5.2 4.0 4.0 6.0 Solder heat resistance (° C.) Normal conditions 300°C. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Moisture absorption 260° C. ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Flameretardancy (UL94, VTM-0) ∘ ∘ ∘ ∘ ∘ x ∘ ∘ ∘ Anti-migration propertiesEvaluation of single layer structure ∘ ∘ ∘ ∘ ∘ x x x x Evaluation ofmultilayer structure ∘ ∘ ∘ ∘ x x x x x Comparative Example MeasurementItem 6 7 8 9 10 Adhesive composition Compara- Compara- Compara- Compara-Compara- tive tive tive tive tive blend blend blend blend blend example6 example 7 example 8 example 9 example 2 Electrically insulating filmPI PI PI PI AR (Polyimide: PI, aramid: AR) Evaluation of copper-cladlaminate Peel strength (N/cm) 5.5 4.2 3.6 3.0 1.5 Solder heat resistance(° C.) Normal conditions 300° C. ∘ ∘ ∘ ∘ ∘ Moisture absorption 260° C. ∘∘ ∘ ∘ ∘ Flame retardancy (UL94, VTM-0) x ∘ x ∘ ∘ Anti-migrationproperties Evaluation of single layer structure ∘ ∘ x x x Evaluation ofmultilayer structure x x x x x Evaluation of coverlay film Peel strength(N/cm) 5.3 4.1 3.6 2.8 1.5 Solder heat resistance (° C.) Normalconditions 300° C. ∘ ∘ ∘ ∘ ∘ Moisture absorption 260° C. ∘ ∘ ∘ ∘ ∘ Flameretardancy (UL94, VTM-0) x ∘ x ∘ ∘ Anti-migration properties Evaluationof single layer structure ∘ ∘ x x x Evaluation of multilayer structure xx x x x<Properties of Adhesive Sheets>

Example 5

Combining the adhesive composition components in the proportions shownin the column labeled “blend example 1” in Table 1, a dispersion wasprepared in the same manner as the example 1. Subsequently, anapplicator was used to apply the dispersion to the surface of arelease-treated polyester film, in sufficient quantity to generate adried coating of the composition with a thickness of 25 μm, and theapplied coating was then dried for 10 minutes at 120° C. in a forced airoven, thereby converting the composition to a semi-cured state, andcompleting preparation of an adhesive sheet.

Comparative Example 11

With the exception of combining the adhesive composition components inthe proportions shown in the column labeled “comparative blend example2” in Table 1, an adhesive sheet was prepared in the same manner as theexample 5.

[Measurements]

The properties of the adhesive sheets prepared in the example 5 and thecomparative example 111 were measured in accordance with the measurementmethods 4 described below. The results of the measurements are shown inTable 3.

—Measurement Methods 4 —

4-1. Peel Strength

An adhesive layer prepared by removing the polyester protective filmfrom the adhesive sheet was sandwiched between a polyimide film B (brandname: Apical, manufactured by Kaneka Corporation, thickness: 75 μm) anda polyimide film C (brand name: Apical, manufactured by KanekaCorporation, thickness: 25 μm), and a press device (temperature: 160°C., pressure: 3 MPa, time: 60 minutes) was then used to bond the film Band the film C together, thereby completing preparation of a pressedsample. This pressed sample was then cut to a width of 1 cm and a lengthof 15 cm to form a test specimen. The polyimide film B (thickness: 75μm) of this test specimen was secured, and the minimum value for theforce required to peel the polyimide film C (thickness: 25 μm) at aspeed of 50 mm/minute in a direction at an angle of 180 degrees to thesurface of the polyimide film B under conditions at 25° C. was thenmeasured, and this measured value was reported as the peel strength.

TABLE 3 Example Comparative example Measurement item 5 11 Peel strength(N/cm) 12.3 5.0<Evaluations>

The compositions prepared in the blend examples 1, 2 and 3 satisfy therequirements of the present invention, and the flexible copper-cladlaminates, coverlay films and adhesive sheets prepared using thesecompositions exhibited excellent levels of peel strength, solder heatresistance, flame retardancy, and anti-migration properties.

The composition prepared in the comparative blend example 1 lacks theion scavenger or heavy metal deactivator (F) required by the presentinvention, and as a result, the anti-migration properties of theevaluated multilayer laminate were poor.

The composition prepared in the comparative blend example 4 does notcontain the phosphate compound (E) and the ion scavenger or heavy metaldeactivator (F) required by the present invention, and exhibited poorlevels of peel strength and anti-migration properties.

The compositions prepared in the comparative blend example 2, thecomparative blend example 6 and the comparative blend example 8 do notcontain the phosphate compound (E) required by the present invention,and exhibited poor levels of peel strength and anti-migrationproperties. Furthermore, because these compositions used aphosphorus-based flame retardant with a lower phosphorus content thanthe phosphate compound (E) of the present invention, although thequantity of flame retardant added was the same as that used in the blendexample 1, the flame retardancy was inferior.

The compositions prepared in the comparative blend example 3, thecomparative blend example 5, the comparative blend example 7 and thecomparative blend example 9 do not contain the phosphate compound (E)required by the present invention and exhibited poor levels of peelstrength and anti-migration properties.

INDUSTRIAL APPLICABILITY

A cured product produced by curing a flame retardant adhesivecomposition of the present invention, together with a coverlay film, anadhesive sheet and a flexible copper-clad laminate produced using such acomposition, all exhibit excellent peel strength, solder heat resistanceand flame retardancy, and moreover, not only exhibit superioranti-migration properties in the type of single layer structure that iswidely used conventionally, but also exhibit superior anti-migrationproperties in multilayer structures with much higher density, and arealso halogen-free, meaning they offer considerable promise inapplications such as the production of environmentally friendly flexibleprinted wiring boards.

1. A flame retardant adhesive composition comprising: (A) a halogen-freeepoxy resin, (B) a carboxyl group-containing acrylic resin and/or acarboxyl group-containing acrylonitrile-butadiene rubber, (C) a curingagent, (E) a phosphate compound represented by a general formula (1)shown below and/or a phosphate compound represented by a general formula(3) shown below:

[wherein, n represents a number from 1 to 100, X₁ represents eitherammonia or a triazine derivative represented by a general formula (2)shown below:

[wherein, Z₁ and Z₂ are the same or different, and each represent agroup selected from the group consisting of groups represented by aformula: —NR₅R₆ (wherein, R₅ and R₆ are the same or different, and eachrepresent a hydrogen atom, a straight-chain or branched alkyl group of 1to 6 carbon atoms, or a methylol group), a hydroxyl group, a mercaptogroup, straight-chain or branched alkyl groups of 1 to 10 carbon atoms,straight-chain or branched alkoxy groups of 1 to 10 carbon atoms, aphenyl group, and a vinyl group], and p is a number that satisfies:0<p≦n+2],

[wherein, r represents a number from 1 to 100, Y₁ represents a diaminerepresented by a formula: R₁R₂N(CH₂)_(m)NR₃R₄ (wherein, R₁, R₂, R₃ andR₄ each represent, independently, a hydrogen atom, or a straight-chainor branched alkyl group of 1 to 5 carbon atoms, and m represents aninteger from 1 to 10), piperazine, or a diamine that contains apiperazine ring, and q is a number that satisfies: 0<q≦r+2], and (F) anion scavenger and/or a heavy metal deactivator.
 2. The flame retardantadhesive composition defined in claim 1, the composition comprising 100parts by mass of the halogen-free epoxy resin (A), from 10 to 200 partsby mass of the carboxyl group-containing acrylic resin and/or carboxylgroup-containing acrylonitrile-butadiene rubber (B), from 0.5 to 20parts by mass of the curing agent (C), sufficient quantity of thephosphate compound represented by the general formula (1) and/or thephosphate compound represented by the general formula (3) that aphosphorus content within the composition, relative to the organic resincomponents within the adhesive composition excluding inorganic solidcomponents, is within a range from 2.0 to 4.0% by mass (E), and from 0.1to 5 parts by mass of the ion scavenger and/or heavy metal deactivator(F).
 3. The flame retardant adhesive composition defined in claim 1,further comprising a curing accelerator (D).
 4. The flame retardantadhesive composition defined in claim 1, wherein the carboxylgroup-containing acrylic resin of component (B) has a glass transitiontemperature (Tg) within a range from −40 to 30° C., comprises anacrylate ester as a primary component, and is formed using the acrylateester and a monomer having a carboxyl group.
 5. The flame retardantadhesive composition defined in claim 1, wherein the carboxylgroup-containing acrylic resin of component (B) is an acrylic polymerobtained by copolymerizing three components, namely (a) an acrylateester and/or methacrylate ester, (b) acrylonitrile and/ormethacrylonitrile, and (c) an unsaturated carboxylic acid.
 6. Anadhesive sheet, comprising a releasable base material, and a layercomprising the adhesive composition defined in claim 1 formed on onesurface of the base material.
 7. The adhesive sheet defined in claim 6,wherein a dried thickness of the layer comprising the adhesivecomposition is within a range from 5 to 50 μm.
 8. A coverlay film,comprising an electrically insulating film, and a layer comprising theadhesive composition defined in claim 1 provided on at least one surfaceof the electrically insulating film.
 9. The coverlay film defined inclaim 8, wherein a thickness of the electrically insulating film iswithin a range from 9 to 50 μm, and a dried thickness of the layercomprising the adhesive composition is within a range from 5 to 45 μm.10. The coverlay film defined in claim 8, wherein the electricallyinsulating film comprises a polyimide film or an aramid film.
 11. Thecoverlay film defined in claim 10, wherein the electrically insulatingfilm comprises a support film and an aramid film with a thickness of 3to 9 μm supported on the support film.
 12. The coverlay film defined inclaim 8, comprising an electrically insulating film that comprises anaramid film with a thickness of 3 to 9 μm supported on a support film, alayer comprising the adhesive composition defined in claim 1 provided onat least one surface of the electrically insulating film, and areleasable base material provided on top of the layer comprising theadhesive composition.
 13. A flexible copper-clad laminate, comprising anelectrically insulating film, a layer comprising the adhesivecomposition defined in claim 1 provided on either one surface or bothsurfaces of the insulating film, and either a single copper foil layeror two copper foil layers provided on top of the one or two layers ofthe adhesive composition.
 14. The flexible copper-clad laminateaccording to claim 13, wherein the electrically insulating filmcomprises a polyimide film or an aramid film.
 15. The flexiblecopper-clad laminate according to claim 13, wherein the electricallyinsulating film comprises a support film and an aramid film with athickness of 3 to 9 μm supported on the support film.
 16. The flexiblecopper-clad laminate defined in claim 13, wherein a dried thickness ofthe layer comprising the adhesive composition is within a range from 5to 45 μm.